1. Field of the Invention
The present invention relates to a communication technique between an image forming apparatus main body and an option apparatus attached to it.
2. Description of the Related Art
Conventionally, a plurality of option apparatuses attachable to an image forming apparatus main body are connected to the image forming apparatus. While communicating with the option apparatuses, the image forming apparatus main body controls them to execute a cooperative operation for sheet feeding/conveyance or sheet delivery/conveyance.
For example, according to Japanese Patent Laid-Open No. 09-193508 (patent reference 1), an image forming apparatus main body communicates with a plurality of option apparatuses to transmit/receive data by serial communication synchronized with common clocks.
Signal lines for clocks and data are commonly connected to a plurality of option apparatuses. In addition, an individual signal line is arranged for each option apparatus to identify a specific option apparatus to be communicated among a plurality of option apparatuses.
When communicating with one specific option apparatus at once, the image forming apparatus main body activates only an individual signal line connected to it and executes communication.
When communicating with all option apparatuses, the image forming apparatus main body activates all signal lines individually arranged for them and performs communication.
Image forming apparatuses in Japanese Patent Laid-Open Nos. 2006-133996 (patent reference 2) and 2006-225108 (patent reference 3) omit individual signal lines, which are arranged for respective option apparatuses in patent reference 1. The image forming apparatus communicates with cascade-connected option apparatuses via a common communication line.
More specifically, when communicating with one specific option apparatus, the image forming apparatus sets an option apparatus identifier in communication data. Upon receiving the communication data, only one of option apparatuses that matches the identifier processes communication.
Japanese Patent Laid-Open No. 2006-270447 (patent reference 4) proposes a method of simultaneously communicating with all option apparatuses. More specifically, an image forming apparatus sets an identifier (also called a broadcast ID) representing all apparatuses in a send command, in addition to an identifier meaning each option. Upon receiving the command, each option apparatus recognizes the broadcast ID and responds to the command.
When accelerating/decelerating a print sheet throughout a plurality of option apparatuses, a conventional image forming apparatus issues an instruction to successively drive the option apparatuses according to, for example, the technique disclosed in patent reference 2 or 3.
In this case, a higher conveyance speed makes “tension” or “flexion” of a print sheet large between option apparatuses and sometimes causes “jamming” because the control instruction communication speed is not so high. These problems are negligible at low conveyance speeds of image forming apparatuses, but become serious at higher conveyance speeds of recent image forming apparatuses.
These problems can be suppressed by simultaneously driving all option apparatuses using a broadcast ID, as described in patent reference 4.
However, as an environmental measure, even image forming apparatuses are recently requested to minimize power consumption.
More specifically, the image forming apparatus needs to simultaneously control conveyance of a print sheet over the first option apparatus group containing some option apparatuses while keeping the remaining option apparatus group still without conveying the print sheet and affecting the conveyance. For example, the first option apparatus group can include option apparatuses 1 and 2, whereas the remaining option apparatus group can include option apparatuses 3 and 4.
The present invention can solve at least one of the above-described problems and others. For example, the present invention controls option apparatuses to smoothly convey a recording medium while suppressing power consumed by conveyance, compared to a conventional technique. The other problems will become apparent throughout the specification.